Lithography techniques include processes in which, for example, a resist film formed from a resist material is formed on top of a substrate, the resist film is selectively exposed to irradiation such as light, an electron beam or the like through a mask in which a predetermined pattern has been formed, and then a developing treatment is conducted, thereby forming a resist pattern of the prescribed shape in the resist film.
Resist materials in which the exposed portions change to become soluble in a developing solution are termed positive materials, whereas resist materials in which the exposed portions change to become insoluble in the developing solution are termed negative materials.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have led to rapid progress in the field of miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used; however, nowadays, KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production of semiconductor elements. Furthermore, research is also being conducted into lithography techniques that use F2 excimer lasers, electron beams (EB), extreme ultraviolet radiation (EUV) and X-rays.
Resist materials are required to have lithography properties such as high sensitivity to the aforementioned light source and sufficient resolution to reproduce patterns with very fine dimensions.
As resist materials which fulfill the aforementioned requirements, there is used a chemically-amplified resist composition containing a base resin that displays changed solubility in an alkali developing solution under action of an acid, and an acid generator that generates an acid upon exposure.
For example, as the chemically-amplified positive resist composition, a composition containing a resin component (a base resin) that exhibits increased solubility in an alkali developing solution under action of an acid and an acid generator component is commonly used. If the resist film formed using the resist composition is selectively exposed during formation of a resist pattern, then within the exposed portions, an acid is generated from the acid generator, and the action of this acid causes an increase in the solubility of the resin component in an alkali developing solution, making the exposed portions soluble in the alkali developing solution.
On the other hand, the chemically-amplified negative resist composition includes, for example, a resin component having a carboxyl group, a cross-linking agent having an alcoholic hydroxyl group, and an acid generator. In the resist pattern formation, the action of an acid generated from the acid generator causes a reaction between the carboxyl group within the resin component and the alcoholic hydroxyl group within the cross-linking agent, thereby changing the resin component from an alkali-soluble state to an alkali-insoluble state.
Resins (acrylic resins) that contain structural units derived from (meth)acrylate esters within the main chain are now widely used as base resins for resists that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 1). Here, the term “(meth)acrylic acid” is a generic term that includes either or both of the acrylic acid having a hydrogen atom bonded to the α-position and the methacrylic acid having a methyl group bonded to the α-position. The term “(meth)acrylate ester” is a generic term that includes either or both of an acrylate ester having a hydrogen atom bonded to the α-position and a methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of an acrylate having a hydrogen atom bonded to the α-position, and a methacrylate having a methyl group bonded to the α-position.
Also, as base resins for chemically-amplified resists, base resins containing a plurality of structural units are now used in order to improve lithography properties and the like. For example, in the case of using a positive-type resist, a base resin is typically used which includes a structural unit having an acid dissociable, dissolution inhibiting group which dissociates under action of an acid generated from an acid generator, and further includes a structural unit having a polar group such as a hydroxyl group, a structural unit having a lactone structure, and the like. Of these structural units, the structural unit having a lactone structure is generally considered to contribute to the improvement of the adhesion of the resist film with a substrate, the improvement of compatibility with an alkali developing solution, and the improvement of lithography properties.